The central aim of this project is to integrate theories of language production and motor action into new accounts of specific language impairment (SLI). SLI is a disorder that affects approximately 7% of children at the time they enter kindergarten. Because of the longstanding adverse academic, social, and communicative consequences of SLI, it is imperative to understand the bases of the disorder for the development of appropriate intervention strategies. Many current approaches to SLI focus exclusively on language factors. Yet language is expressed through movement, and deficits in limb motor skill have been implicated in children with SLI. Current neurophysiological hypotheses about relations between language and action further support a rethinking of how these domains interact in normal and disordered development. The present studies assess whether the well documented co-occurrence between language and limb motor deficits results either from a disorder involving common mechanisms that influence both language and motor processing or rather are independent disorders that tend to appear in tandem (i.e., a co-morbidity). As a related aim, we follow the co- occurrence of language and limb motor deficits longitudinally from the preschool into the school years to track how early limb motor deficits predict outcome. We hypothesize that there are shared mechanisms that underlie the language and the motor deficits observed in SLI. That is, more general difficulties in sequencing, timing, and learning underlie both the grammatical and lexical retrieval deficits that are the hallmark of SLI and the co- occurring limb motor deficits. However, it is also possible that language and motor deficits are independent of each other and that a more general co-morbidity explains why these domains both tend to be affected in children with SLI. To investigate language, speech motor, and limb motor development in children with SLI, we incorporate measures and analyses from both psycholinguistics and speech motor control. The ultimate goal of this research is to translate scientific discoveries about language production and motor action into designing appropriate intervention programs for young children with language impairment. For example, if a common mechanism, such as timing or sequencing, is found to underlie deficits in language processing and limb movement, a more general intervention approach targeted toward this aspect of procedural memory would be indicated. PUBLIC HEALTH RELEVANCE: Children with specific language impairment have longstanding deficits that affect their language development along with their social adjustment and academic achievement. The goal of this research is to translate recent scientific discoveries about language production and motor action into understanding the mechanisms that underlie specific language impairment and into designing appropriate intervention programs for these children.